<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
    /*变量：
    在程序执行的过程中可以改变值
    声明变量 let(ES6)*/
   /* let num1=100;//声明变量并赋值
    let str1,str2='hello';//声明多个变量
    const userName='admin';
    userName='xiaoming';
    console .log (userName)*/

    let flag=true;
    console .log(flag);//true
    console .log (typeof(flag));//数据类型
    let num=123,num1=456;num2=0x23;
    console .log(num );
    console .log(num1 );
    console .log (typeof(num ));
    console .log (typeof(num1 ));
    console .log(num2 );
    console .log (typeof(num2 ));
    console.log ('---------');
    let str1='',str2='hello',str3="javascript";
    console .log(str1 );
    console .log(str2  );
    console .log(str3 );
    console .log(typeof(str1) );
    console .log(typeof(str2) );
    console .log(typeof(str3) );
     //在双引号中使用双引号或在单引号中使用单引号要使用转义符\进行转义。
    let str4="子曰（\"老子\"）：学而时习之，不亦说乎";
    console .log(str4 );
    console .log(typeof(str4) );
    console.log ('---------');
    let n1=null,n2;
    console.log(n1);
    console.log(n2);

</script>
</html>